1. Field of the Invention
This invention relates to the production of bromine by the oxidation of bromide salts in the presence of silicon dioxide and inorganic oxidation catalysts at high temperature, which is a useful process step in the production of ethylene dichloride.
2. Brief Description of the Prior Art
Processes are well known in the art for producing bromine from bromide salts such as the electrolysis of brine solutions containing bromide salts or subjecting the brine solution to gaseous chlorine in which chlorine oxidizes the soluble bromide salts to bromine.
The disadvantages of producing bromine from aqueous solutions of bromide salts by electrolysis are the cost of required electricity plus the complex electrolysis apparatus that is required, and the disadvantages in producing bromine from the chlorine oxidation of bromide salts are the use of highly toxic chlorine plus the difficulty in obtaining product bromine which is not contaminated with hydrochloric acid, hydrobromic acid or chlorine.
A proces is described in British Pat. No. 930,341 (1963) for converting aqueous hydrobromic acid to bromine by oxidation with a stream of air in the presence of a copper or iron catalyst. This method has the disadvantage of requiring the acidification of aqueous solutions of bromide salts prior to oxidation and also does not allow the oxidation to be carried out on solid bromide salts.
It is known that elemental bromine can be produced from heating a mixture of potassium bromide and clay comprised of aluminum silicate as exemplified in A. Gorgeu, Comptes rendus 102, 1164-7 (1886). However, the yields are not stated and the use of an aluminum silicate clay does not produce a by-product silicate such as sodium/calcium silicate that is useful in the glass industry, and which would render the process more economical.
A process is known in the prior art for producing alkali metal hydroxides by heating a mixture of an alkali metal salt, sand and phosphoric acid or boric acid with steam, as disclosed in The Chemical Trade Journal and Chemical Engineer, page 102 (Aug. 7, 1936); however, the process is not suitable for producing bromine.
Attempts in the prior art have been unsuccessful for developing a procedure which will produce high yields of bromine and by-product silicates useful in the glass industry by heating alkali metal bromides in the presence of silicon dioxide at high temperature, as disclosed by C. F. Schoenbein, Annalen der Physik 78, 513-23 (1849), where only a trace of bromine was formed under the conditions of the reaction.
Thus, a process is desired for converting solid bromide salts to bromine in high yield in the presence of silicon dioxide, which does not require mineral acids, electrolysis or the use of chlorine gas, and wherein a by-product silicate is formed which is useful in the glass industry.